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United States Patent |
5,622,206
|
Takeuchi
,   et al.
|
April 22, 1997
|
Multiple valve unit for pressurized fluid supply system
Abstract
A multiple valve includes first and second valve units respectively having
first and second valve bodies. The first and second valve bodies have
respective spool bores therein; and a respective spool is inserted in the
spool bore of each of the first and second valve bodies. The first and
second valve bodies of the first and second valve units also have inlet
ports, tank ports, and first and second blocks having mounting holes, the
blocks and a respective valve body being fixedly coupled together by means
of stud bolts. The first block has a first threaded hole on one side
surface thereof for receiving the stud bolt, and a second threaded hole on
another side surface thereof for receiving a cover bolt. A pump passage, a
main passage and a tank passage extend between the one side surface and
the another side surface of the first block, and a stud bolt extends
through the second block and is engaged with the first threaded hole. A
cover is fixedly mounted on the another side surface of the first block by
a cover bolt which is engaged with the second threaded hole, the cover
having a cut-out groove therein for communicating the pump passage with
the main passage.
Inventors:
|
Takeuchi; Masamitsu (Kawasaki, JP);
Ikei; Kazunori (Kawasaki, JP);
Karakama; Tadao (Kawasaki, JP);
Akashi; Mitsumasa (Kawasaki, JP);
Akiyama; Teruo (Kawasaki, JP);
Maruyama; Jun (Kawasaki, JP);
Taka; Keisuke (Kawasaki, JP)
|
Assignee:
|
Kabushiki Kaisha Komatsu Seisakusho (Tokyo, JP)
|
Appl. No.:
|
552693 |
Filed:
|
November 3, 1995 |
Foreign Application Priority Data
| Apr 08, 1992[JP] | 4-29640 U |
| May 29, 1992[JP] | 4-161925 |
| May 29, 1992[JP] | 4-161926 |
Current U.S. Class: |
137/596; 137/884 |
Intern'l Class: |
F15B 013/08 |
Field of Search: |
137/596,884
|
References Cited
U.S. Patent Documents
4020867 | May., 1977 | Sumiyoshi | 91/446.
|
4709724 | Dec., 1987 | Williams | 137/596.
|
5038671 | Aug., 1991 | Ueno | 91/517.
|
5115835 | May., 1992 | Ueno | 137/596.
|
5138837 | Aug., 1992 | Obertrifter et al. | 91/446.
|
Foreign Patent Documents |
3331483A1 | Dec., 1984 | DE.
| |
3701211A1 | Aug., 1987 | DE.
| |
3844400A1 | Jul., 1990 | DE.
| |
60-11706 | Jan., 1985 | JP.
| |
62-202574 | Dec., 1987 | JP.
| |
3-144023 | Jun., 1991 | JP.
| |
Primary Examiner: Michalsky; Gerald A.
Attorney, Agent or Firm: Frishauf, Holtz, Goodman, Langer & Chick
Parent Case Text
This is a division of application Ser. No. 08/302,912, filed as
PCT/JP93/00452 Apr. 8, 1993, now U.S. Pat. No. 5,533,334.
Claims
We claim:
1. A multiple valve assembly comprising:
a plurality of valves each having a valve body;
each of said valve bodies comprising a spool bore provided therein;
a spool inserted in each of said spool bores;
each of said valve bodies further comprising an inlet port, a tank port, a
pump passage, a main passage, a tank passage and a bolt receptacle hole
extending through opposite sides of each of said valve bodies;
a first block and a second block each having a mounting hole, an inlet port
and a tank port;
said first block comprising:
a first threaded hole on a first side surface of said first block, and a
second threaded hole on a second side surface of said first block; and
a pump passage, a main passage and a tank passage extending between said
first and second side surfaces of said first block;
a stud bolt extending through said second block and through said bolt
receptacle holes of said valve bodies, said stud bolt being engaged with
said first threaded hole of said first block to fixedly couple together
said first block, said plurality of valves and said second block; and
a cover mounted on said second side surface of said first block by a cover
bolt which is engaged with said second threaded hole of said first block,
said cover having a passage therein for communicating said pump passage of
said first block with said main passage of said first block.
2. The multiple valve assembly of claim 1, wherein said pump passage, said
main passage and said tank passage in each of said valve bodies and said
first block are respectively coupled to each other for communication
therebetween.
3. The multiple valve assembly of claim 1, wherein said bolt receptacle
holes of said valve bodies are axially aligned with each for insertion of
said stud bolt therethrough.
4. The multiple valve assembly of claim 1, wherein said stud bolt and said
cover bolt respectively threadingly engage said first and second threaded
holes of said first block.
5. The multiple valve assembly of claim 1, wherein at least two of said
plurality of valves are adjacent to each other and said first side surface
of said first block is mounted on a first side of said adjacent valves and
said second block is mounted on a second side of said adjacent valves
opposite said first side.
6. The multiple valve assembly of claim 5, wherein said cover is removably
mounted on said second side surface of said first block.
7. The multiple valve assembly of claim 6, wherein an additional valve is
mountable on said second side surface of said first block, and said cover
is mountable on said additional valve by means of a long cover bolt which
extends through a bolt receptacle hole of a valve body of said additional
valve, said long cover bolt engaging with said second threaded hole of
said first block.
8. The multiple valve assembly of claim 1, wherein said plurality of valves
comprise at least a first valve and a second valve which is different than
said first valve.
9. The multiple valve assembly of claim 1, wherein said passage provided in
said cover comprises a groove.
10. A multiple valve assembly comprising:
a plurality of adjacent valves each having a valve body;
each of said valve bodies comprising a spool bore provided therein;
a spool inserted in each of said spool bores;
each of said valve bodies further comprising an inlet port, a tank port, a
pump passage, a main passage, a tank passage and a bolt receptacle hole
extending through opposite sides of each of said valve bodies;
a first block and a second block each having a mounting hole, an inlet port
and a tank port;
said first block comprising:
a first threaded hole on a first side surface of said first block, and a
second threaded hole on a second side surface of said first block; and
a pump passage, a main passage and a tank passage extending between said
first and second side surfaces of said first block;
a stud bolt extending through said second block and through said bolt
receptacle holes of said valve bodies of said plurality of adjacent
valves, said stud bolt being engaged with said first threaded hole of said
first block to fixedly couple together said first block, said plurality of
adjacent valves and said second block;
an additional valve having a valve body, said valve body of said additional
valve comprising a tank passage, a main passage, a pump passage, and a
bolt receptacle hole extending through opposite sides of said valve body
of said additional valve;
said additional valve being mounted on said second side surface of said
first block; and
a cover mounted on said additional valve by a cover bolt which extends
through said bolt receptacle hole of said valve body of said additional
valve, said cover bolt engaging with said second threaded hole of said
first block.
11. The multiple valve assembly of claim 10, wherein said pump passage,
said main passage and said tank passage in each of said first block and
said valve bodies of said plurality of adjacent valves and said additional
valve are respectively coupled to each other for communication
therebetween.
12. The multiple valve assembly of claim 10, wherein said bolt receptacle
holes of said valve bodies of said plurality of adjacent valves are
axially aligned with each for insertion of said stud bolt therethrough.
13. The multiple valve assembly of claim 10, wherein said stud bolt and
said cover bolt respectively threadingly engage said first and second
threaded holes of said first block.
14. The multiple valve assembly of claim 10, wherein said plurality of
valves comprise at least a first valve and a second valve which is
different than said first valve.
15. The multiple valve assembly of claim 10, wherein said cover comprises a
passage provided therein for communicating said pump passage of said first
block with said main passage of said first block.
16. The multiple valve assembly of claim 15, wherein said passage provided
in said cover comprises a groove.
Description
FIELD OF THE INVENTION
The present invention relates to a hydraulic pressure supply system for
distributing a pressurized fluid discharged from one or more hydraulic
pumps to a plurality of actuators. More specifically, the invention
relates to a pressurized fluid supply system for distributing a
pressurized fluid discharged from one or more hydraulic pumps to left and
right hydraulic motors for traveling and a work implement cylinder.
BACKGROUND ART
Japanese Unexamined Patent Publication (Kokai) No. Showa 60-11706 discloses
a pressurized fluid supply system of the type set forth above. FIG. 1
shows the pressurized fluid supply system disclosed in the
above-identified publication. A plurality of pressure compensation valves
3 and 13 are connected in parallel to a discharge line pipe 2 of a
hydraulic pump 1. Discharge pipes 4 and 14 of respective pressure
compensation valves 3 and 13 are provided with direction control valves 5
and 15. The outlet sides of the direction control valves 5 and 15 are
connected to actuators 6 and 16. The pressure compensation valves 3 and 13
are constructed to be biased in valve opening direction by a pump
discharge pressure and outlet pressures of the direction control valves 5
and 15 and to be biased in valve closing direction by the inlet pressures
of the direction control valves and the highest load pressure. With the
shown pressurized fluid supply system, it becomes possible to supply
pressurized fluid discharged from the pump to respective actuators at a
predetermined distribution ratio when a plurality of direction control
valves 3 and 13 are operated simultaneously.
However, in the above-mentioned pressurized fluid supply system, it becomes
essential to provide a shuttle valve 7 for comparing load pressures of
respective actuators and supplying the highest load pressure to the
pressure compensation valves. Furthermore, the number of shuttle valves
required becomes one less than the number of actuators. Therefore, the
number of necessary shuttle valves is inherently increased according to
increasing of the number of the actuators to be supplied with the
pressurized fluid thus increasing cost.
On the other hand, in the pressurized fluid supply system illustrated in
FIG. 1, assuming that the load pressure of the actuator 6 is higher than
the load pressure of the actuator 16 among the load pressures generated
upon actuation of two actuators 6 and 16, a pressure in a passage 6 is
introduced into a passage 9 via the shuttle valve; as the maximum load
pressure. Subsequently, if the load pressure fluctuates and the load
pressure of the actuator 16 becomes higher than the load pressure of the
actuator 6, the shuttle valve 7 is switched to connect the passage 9 and a
passage 18. Upon this switching, due to blow off of the shuttle valve 7,
the pressure in the passage 16 drops, and the pressure in the other
passage 8 is blocked. As a result, upon switching of the shuttle valve 7,
the actuator 6 transitively causes a natural drop and the natural drop is
accelerated.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above-mentioned problem
in the prior art and thus to provide a pressurized fluid supply system
which can distribute pressurized fluid discharged from a hydraulic pump to
a plurality of actuators without employing any shuttle valve.
Another object of the invention is to provide a pressurized fluid supply
system which can prevent transitive natural drop of an actuator upon
switching between load pressures.
A further object of the invention is to provide a pressurized fluid supply
system which can prevent a discharge amount of the hydraulic pump from
being excessively decreased by generating a control pressure lower than a
pressure corresponding to a load on a work implement even when the work
implement is operated during travel of a working vehicle, and prevent
abrupt variation of flow rates of the pressurized fluid supplied to left
and right hydraulic motors so as not to cause excessive deceleration
shock.
In order to accomplish the above-mentioned objects, according to the first
aspect of the invention, a pressurized fluid supply system, in which a
plurality of pressure compensation valves are connected to a pump
discharge line of a hydraulic pump in parallel, direction control valves
being provided at the outlet side of each pressure compensation valves to
supply a discharged pressurized fluid from the hydraulic pump to a
plurality of actuators, comprises:
the pressure compensation valve being provided a check valve portion
establishing and blocking communication between the pump discharge line
and the inlet port of the direction control valve, and a pressure
reduction valve portion reducing the pressure of the pump discharge
pressure;
the check valve portion being constructed for shifting in a valve opening
direction in response to an inlet pressure and shifting in a valve closing
direction in response to an outlet pressure;
the pressure reduction valve portion being contacted with the check valve
portion by means of a spring, urged by a pressure of one pressure chamber
for communicating between inlet side and outlet side and shifting away
from the check valve portion, and urged by a pressure of the other
pressure chamber for blocking communication between the inlet side and the
outlet side and biasing the check valve portion in the valve closing
direction; and
a load pressure of the actuator, to which the pressurized fluid is
supplied, being introduced into the one pressure chamber and communicating
between the other pressure chambers of respective valve blocks.
According to the second aspect of the invention, a pressurized fluid supply
system comprises:
a valve block;
a direction control valve constructed by forming a spool bore, a check
valve receptacle bore and a reduction valve receptacle bore in the valve
block, opening a pump port, first and second load pressure detection
ports, first and second actuator ports and first and second tank ports to
the spool bore, and slidably inserting a main spool in the spool bore for
selectively establishing and blocking communication between the respective
ports;
a check valve portion forming in the valve block a fluid passage
communicating a first port opening to the check valve receptacle bore and
the pump port, and inserting a spool for establishing and blocking
communication between the first port and the fluid passage in the check
valve receptacle bore, the spool being stopped at the blocking position;
a pressure reduction valve portion constructed by forming second and third
ports opening to the pressure reduction valve receptacle bore in the valve
block, defining first and second pressure chambers at opposite ends of a
spool inserted in the pressure reduction valve receptacle bore, the first
pressure chamber being communicated with the second load pressure
detection port and the second pressure chamber being communicated with the
third port, and contacting the spool disposed within the pressure
reduction valve receptacle bore to the check valve and biasing the same in
the valve closing direction of the check valve portion by a spring;
the check valve portion and the pressure reduction valve portion forming a
pressure compensation valve;
the configuration of the spool of the pressure reduction valve portion
being a configuration for establishing communication between the first
pressure chamber and the second port when the spool slides against the
spring force of the spring by the pressure of the first pressure chamber;
and
a discharge line of a hydraulic pump being connected to the first ports of
a pair of valve blocks, second ports of a pair of valve blocks being
communicated with each other, and third ports of a pair of valve block
being communicated with a load detection passage.
According to the third aspect of the invention, a pressurized fluid supply
system for distributing pressurized fluid to actuators constituted of a
pair of left and right hydraulic motors for driving left and right driving
wheels and a actuator constituted of a work implement cylinder for driving
a work implement, comprises:
a valve block;
a direction control valve constructed by forming a spool bore, a check
valve receptacle bore and a reduction valve receptacle bore in the valve
block, opening a pump port, first and second load pressure detection
ports, first and second actuator ports and first and second tank ports to
the spool bore, and slidably inserting a main spool in the spool bore for
selectively establishing and blocking communication between the respective
ports;
a check valve portion forming in the valve block a fluid passage
communicating a first port opening to the check valve receptacle bore and
the pump port, and inserting a spool for establishing and blocking
communication between the first port and the fluid passage in the check
valve receptacle bore, the spool being stopped at the blocking position;
a pressure reduction valve portion constructed by forming second and third
ports opening to the pressure reduction valve receptacle bore in the valve
block, defining first and second pressure chambers at opposite ends of a
spool inserted in the pressure reduction valve receptacle bore, the first
pressure chamber being communicated with the second load pressure
detection port and the second pressure chamber being communicated with the
third port, and contacting the spool disposed within the pressure
reduction valve receptacle bore to the check valve and biasing the same in
the valve closing direction of the check valve portion by a spring;
the check valve portion and the pressure reduction valve portion forming a
pressure compensation valve;
in the spool of the pressure reduction valve portion of a pair of valve
blocks supplying the pressurized fluid for the hydraulic motors for
traveling, a communication passage for communicating the third port and
the first pressure chamber being formed and a check valve which opens when
the pressure of the third port is higher than the pressure of the second
portion, being provided in the communication passage;
a discharge line of a hydraulic pump being connected to the first port of
the pair of valve blocks and to first and second ports of the valve block
for supplying the pressurized fluid for the work implement cylinder, the
third port of each of the valve blocks being connected to a load detection
passage, and the second ports of the pair of left and right valve blocks
being communicated with each other.
According to a fourth aspect of the invention, a pressurized fluid supply
system for distributing pressurized fluid from a pressurized fluid source
to a first hydraulic load and a second hydraulic load at first and second
line pressures depending upon respective load pressures, comprises:
first valve means for supplying the first line pressure to the first
hydraulic load;
second valve means for supplying the second line pressure to the second
hydraulic load;
first load pressure introducing means connected to the first hydraulic load
for introducing a first load pressure;
second load pressure introducing means connected to the second hydraulic
load for introducing a second load pressure;
first line pressure generating means disposed between the pressurized fluid
source and the first valve means and connected to the first load pressure
introducing means for generating a first line pressure on the basis of a
supply pressure supplied from the pressurized fluid source and the first
load pressure for supplying the first valve means with the first line
pressure;
second line pressure generating means disposed between the pressurized
fluid source and the second valve means and connected to the second load
pressure introducing means for generating a second line pressure on the
basis of a supply pressure supplied from the pressurized fluid source and
the second load pressure for supplying the second valve means with the
second line pressure; and
discharge pressure control means for controlling discharge pressure of the
pressurized fluid source depending upon the first and second line
pressures generated by the first and second line pressure generating
means.
The first and second valve means may comprise direction control valves for
reversing operating directions of corresponding first and second hydraulic
loads by reversing supply direction of the pressurized fluid. Also, the
first and second line pressure generating means may comprise pressure
compensation valves, each having a check valve portion and a pressure
reduction valve portion.
In the preferred construction, the pressure reduction valve portion has a
load pressure feedback chamber and a supply pressure chamber opposing to
opposite ends of a pressure reduction valve body, and shifting the
pressure reduction valve body depending upon the load pressure introduced
via corresponding one of the first and second load pressure introducing
means for establishing and blocking communication between the supply
pressure chamber and the pressurized fluid source to generate a pilot
pressure to be supplied to the discharge pressure control means. Also, it
is preferred that the check valve portion comprises a valve opening side
pressure chamber exerting a supply pressure of the pressurized fluid
source to a check valve body in valve opening direction, and means for
exerting a force corresponding to a pressure difference between the
pressure of the load pressure feedback chamber of the pressure reduction
valve portion and the pressure of the supply pressure chamber to the check
valve body in valve closing direction, for generating the first and second
line pressures depending upon the supply pressure and the pressure
difference.
Furthermore, the pressure reduction valve body of the pressure reduction
valve portion may be constructed to displace depending up the pressure
difference between the pressure of the load pressure feedback chamber and
the pressure of the supply pressure chamber, the pressure reduction valve
body being shifted in opening direction when the pressure of the load
pressure feedback chamber becomes higher beyond a predetermined pressure
difference relative to the pressure of the supply pressure chamber, for
establishing communication between the pressurized fluid source and the
supply pressure chamber. Also, the pressure reduction valve portion may be
provided with a supply side port communicated with the supply pressure
chamber and a feedback side port communicated with the load pressure
feedback chamber at the valve open position, the supply side port of the
first line pressure generating means and the supply side port of the
second line pressure generating means are communicated with each other,
and the feedback side ports of the first and second line pressure
generating means are commonly connected to the discharge pressure control
means. Furthermore, the pressure reduction valve portion may be provided
with a supply side port communicated with the supply pressure chamber and
a feedback side port communicated with the load pressure feedback chamber
at the valve open position, a communication passage for communicating the
feedback side port to the supply side chamber, and a check valve is
disposed in the communication passage so that the check valve opened when
the pressure at the feedback side port is higher than the pressure of the
supply side port.
According to the fifth aspect of the invention, a multiple valve, including
first and second valve means respectively constructed by inserting spools
in spool bores of first and second valve bodies, the first and second
valve bodies of the first and second valve means being provided with inlet
ports, tank ports and first and second blocks having mounting holes, the
blocks and respective valve body being fixedly coupled by means of stud
bolts, comprises:
the first block being formed with a threaded hole for the stud bolt on one
side surface, and a threaded hole for a cover bolt on the other side
surface, the first block being formed with a pump passage, a main passage
and a tank passage extending between the one side surface and the other
side surface, a stud bolt extending through the second block being engaged
with the threaded hole for the stud bolt, and a cover having a cut-out
groove for communicating the pump passage and the main passage is fixedly
mounted on the other side surface of the first block by engaging a cover
bolt to the threaded hole for the cover bolt.
In the construction set forth above, each of the valve body may be formed
with a pump passage, a main passage, a tank passage and a bolt receptacle
hole extending through opposite sides thereof, the valve body may be
arranged at the other side surface of the first block, the cover is
arranged to the valve body arranged at the other side surface of the first
block the cover and the valve body may be mounted by passing a longer
cover bolt though the cover and the bolt receptacle hole and by engaging
the cover volt to the threaded hole for the cover bolt.
BRIEF DESCRIPTION OF THE DRAWING
The present invention will be understood more fully from the detailed
description given herebelow and from the accompanying drawings of the
preferred embodiment of the present invention, which, however, should not
be taken to be limitative to the invention, but are for explanation and
understanding only.
In the drawings:
FIG. 1 is a hydraulic system diagram showing one example of the
conventional pressurized fluid supply system;
FIG. 2 is a hydraulic system diagram of the first embodiment of a
pressurized fluid supply system according to the present invention;
FIG. 3 is a section showing an embodiment of a pressure compensation valve
and a pressurized fluid supply system;
FIG. 4 is an illustration showing a relationship between a pump discharge
pressure and a pump discharge amount of a hydraulic pump at traveling
state and traveling and work implement operating state;
FIG. 5 is a section of a pressurized fluid supply valve block for a
hydraulic motor for traveling to be employed in the second embodiment of
the invention;
FIG. 6 is a section of a pressurized fluid supply valve block for a work
implement cylinder to be employed in the second embodiment of the
invention;
FIG. 7 is a hydraulic circuit diagram of the second embodiment of a
pressurized fluid supply system of the present invention, to which the
valve blocks of FIGS. 5 and 6 are connected;
FIG. 8 is a cross section showing an embodiment of the pressurized fluid
supply system according to the invention employing a multiple valve;
FIG. 9 is a plan view showing another embodiment of the multiple valve;
FIG. 10 is a front elevation of the multiple valve of FIG. 9;
FIG. 11 is a section taken along line XI--XI of FIG. 9;
FIG. 12 is a plan view showing a condition where one valve block is added;
FIG. 13 is a front elevation showing a condition where one valve block is
added; and
FIG. 14 is a section taken along line XIV--XIV of FIG. 12.
BEST MODE FOR IMPLEMENTING THE INVENTION
The preferred embodiments of the present invention will be discussed
hereinafter with reference to FIG. 2 and subsequent figures.
As shown in FIG. 2, a pressurized fluid supply system is provided with a
plurality of direction control valves 22 in a discharge line 21 of a
hydraulic pump 20. At the inlet side of each direction control valve 22, a
pressure compensation valve formed with check valve 23 and a pressure
reduction valve portion 24 is provided. The direction control valve 22 and
the pressure compensation valve 25 are formed as an integral unit as shown
in FIG. 3.
As shown in FIG. 3, a valve block 30 is formed into a substantially
parallel piped configuration. In the vicinity of the upper portion of the
valve block 30, a spool bore 31 is formed. The spool bore 31 opens at left
and right side surfaces 32 and 33. First and second actuator ports 34 and
35 open to the spool bore 31 at respective inner ends thereof and open to
the upper surface of the valve block 31. In the vicinity of the lower
portion of the valve block 30, a check valve receptacle bore 37 opening at
the left side surface 32 and a pressure reduction valve receptacle opening
37 opening to the right side surface 33 are formed in alignment with each
other. A first port 39 opens to the check valve receptacle bore 37 at the
inner end thereof and to respective front and rear surfaces of the valve
block at the outer end portions. Similarly, the second and third ports 42
and 43 are open to the reduction valve receptacle bore 38 at respective
inner end portions, and to the front and rear surfaces of the valve block
30 at the outer ends, respectively. These first, second and third ports
39, 42 and 43 are adapted to communicate with respective of first, second
and third ports 39, 42 and 43 of adjacent valve block when a plurality of
valve blocks 30 are connected in longitudinal direction to form a
multi-stage valve construction.
The valve block 30 is further formed with a pump port 44 opening to the
spool bore 31, first and second load pressure detecting ports 45 and 46,
the first and second actuator ports 34 and 35, and first and second tank
ports 47 and 48. In the spool bore 31, a main spool 49 is received in
slidable fashion. The main spool 49 has first and second small diameter
portions 50 and 51 and a communication groove 52. Furthermore, the main
spool 49 is formed of a first fluid passage 53 constantly communicating
the first and second load pressure detection ports 45 and 46 and a second
fluid passage 54 selectively communicating and blocking between the second
load pressure detection portion 48 and the second tank port 48. The main
spool 49 is biased toward a neutral position by means of a spring. At the
neutral position, the main spool 49 blocks respective ports, and
communicates the second load pressure detection port 46 and the second
tank port 48 via the second fluid passage 54. The main spool 49 slides
laterally. At a first pressurized fluid supply position where the main
spool 49 is shifted toward the right, the second actuator port 35 is
communicated with the second tank port via the second small diameter
portion 51, and the first actuator port 34 is communicated with the first
load pressure detection port 45 via the first small diameter portion 50.
Also, the communication between the first load detection port 46 and the
second tank port 48 is blocked. On the other hand, at the second
pressurized fluid supply position where the main spool 49 is shifted
toward left, the first actuator port 34 and the first tank port 47 are
communicated via the first small diameter portion 50, the second actuator
port 35 is communicated with the second load pressure detection port 46
via the second small diameter portion 51, and communication between the
first load pressure detection port 46 and the second tank port 48 is
blocked. The spool bore 31 and the main spool 49 form the direction
control valve 22 with the construction set forth above.
On the other hand, the check valve receptacle bore 37 is communicated with
pump port 44 via a fluid passage 56. For the check valve receptacle bore
37, a check valve 60 is engaged for selectively communicating and blocking
between the first pump port 39 and the pump port 44. The check valve 80 is
restricted sliding movement toward left beyond the shown position by means
of a stopper rod provided on a plug 61, and is normally placed at a
blocking position. With this check valve receptacle bore 37 and the check
valve 60, the check valve portion 23 is formed.
The pressure reduction valve receptacle bore 38 is communicated with the
second load pressure detecting port via a fourth port 57 and a fluid
passage 58. In the pressure reduction valve receptacle bore 38, a spool 64
is slidably inserted to form a first pressure chamber 65 and a second
pressure chamber 66. The first pressure chamber 65 is communicated with
the fourth port 57, and the second pressure chamber 66 communicates with a
third port. The spool 64 is formed with a blind bore 67. In the blind bore
67, a free piston 68 is inserted. The free piston 68 is biased toward a
plug 70 by means of a spring 69 inserted in the bottom portion of the
blind bore 67. Furthermore, the spool 64 is formed integrally with a push
rod 71. The push rod 71 is inserted through a through opening 72 formed in
a partitioning wall of the valve block 30 and contact its tip end to the
check valve 60. The spool 64 is further formed with an orifice 73 for
communicating the second port 42 and the blind bore 67. With the
construction set forth above, the pressure reduction valve portion 24 is
formed. Furthermore, with this pressure reduction valve portion 24 and the
check valve portion 23, the pressure compensation valve 25 is formed.
As shown in FIG. 2, the discharge line 21 of the hydraulic pump 20 is
communicated with the first and second ports 39 and 42, the third port 43
is connected to the load pressure detecting passage 82, and the first and
second actuator ports 34 and 35 are connected to actuators 88. It should
be noted that, in FIG. 2, the reference numeral 83 denotes a swash plate
for controlling discharge amount of a hydraulic pump 80, 84 denotes a
servo cylinder, and 85 denotes a direction control valve for adjusting the
pump.
The operation of the preferred embodiment of the pressurized fluid supply
system illustrated in FIG. 2 will be discussed in terms of respective
operation modes.
(1) When Spool of Direction Control Valve 22 is in Neutral Position
A working fluid sucked from a tank 86 by the hydraulic pump 20 is
introduced into the opening side pressure chamber a of the check valve 23
via the discharge line 21. At this time, the pressure chambers 65 and 66
of the pressure reduction valve 24 are open to the tank 86. Accordingly,
the pressures in the pressure chambers 65 and 66 are held at the
atmospheric pressure (hydraulic pressure is zero). At this condition, the
spool 64 of the pressure reduction valve 24 is biased toward the check
valve portion 23 by a relatively small spring force of a spring 69. Then,
the push rod 71 is simply contacted to the check valve 60.
On the other hand, the discharge pressure of the hydraulic pump 20 is
maintained a pressure difference relative to the pressure in the load
pressure detection passage 82 constant by a spring 87 of the direction
control valve 85 for adjusting the pump. Here, assuming that the pressure
difference is 20 kg/cm.sup.2, since the pressure in the load pressure
detecting passage 82 is held at atmospheric pressure (zero), the pump
discharge pressure is risen up to 20 kg/cm.sup.2. In conjunction
therewith, the pump discharge pressure is introduced into the pressure
chamber a of the check valve portion 23 to shift the check valve 60 until
the inlet pressure (outlet pressure of the check valve portion 23) of the
direction control valve 22 becomes equal to the pump discharge pressure.
When the pump discharge pressure and the inlet pressure of the direction
control valve 22 become equal to each other, the shift of the check valve
60 is stopped at a condition contacting with the push rod 71 of the spool
64 of the pressure reduction valve portion 24 by the spring 69.
The pressure reduction valve portion 24 establishes a fluid communication
between the discharge line 21 of the hydraulic pump 20 with the pressure
chamber 66 only at the stroke end. On the other hand, the check valve 23
communicates the pump discharge line 21 to the outlet side. Accordingly,
while the direction control valve 22 is in the neutral position, the pump
discharge line 21 and the pressure chamber 88 will never been established,
and the pressure in the pressure chamber 65 is maintained at zero
(atmospheric pressure).
(2) When Spool of Only One of Direction Control valves 22 is in First
Pressurized Fluid Supply Position B
Here, it is assumed that the spool of the left side direction control valve
22 is shifted to the first pressurized fluid supply position B, and the
spool of the right side direction control valve 22 is maintained at the
neutral position A.
By the shift of the spool of the direction control valve 22, the pump port
44 and the first actuator port 34 are connected. At the same time, the
second actuator port 35 and the second tank port 48 are connected. At this
time, when the pressure (load pressure) in a conduit 89 connecting the
first actuator port 34 and the actuator 88 is greater than the pump
discharge pressure (20 kg/cm.sup.2), the check valve 60 of the check valve
portion 23 is seated by the pressure of the pressure chamber b, the
natural drop of the actuator 88 can be prevented.
The pressure of the conduit 89 of the actuator 88, namely, the load
pressure is introduced into one pressure chamber 65 of the pressure
reduction valve portion 24 via the first fluid passage 53 and the path 58.
At this time, since the pressure of the other pressure chamber 66 becomes
zero, the spool 64 of the pressure reduction valve portion 24 shifts to
the stroke end in the side remote from the check valve portion. By this,
the pump discharge passage 21 and the load pressure detecting path 82 are
communicated with each other via the throttle valve of the pressure
reduction valve 24. When the pressure in the conduit 89 is higher than the
pump discharge pressure (20 kg/cm.sup.2), the check valve 60 of the check
valve portion 23 is blocked by the pressure in the pressure chamber b, and
this pressure is introduced into one pressure chamber 65 of the pressure
reduction valve portion 24. Accordingly, even when the other pressure
chamber 66 is communicated with the pump discharge line 21, the spool of
the pressure reducing valve 24 is maintained in the shifted position. On
the other hand, when the pressure (load pressure) in the passage 41 is
lower than the pump discharge pressure, the load pressure is introduced
into one pressure chamber 65 of the pressure reduction valve portion 24.
By this, the spool 64 of the pressure reduction valve portion 24 shifts in
response to the pressure of the pressure chamber 65. On the other hand,
when the pressure in the other pressure chamber 66 is risen to the
pressure (namely, load pressure) of one pressure chamber 65, the pressure
reduction valve portion 24 becomes blocked state by the small spring force
of the spring 69 to contact the push road 71 to the check valve 60 of the
check valve portion 23.
In either case, the pressure reduction valve portion 24 maintains
communication between the pump discharge line 21 and the pressure chamber
66 until the pressure of one pressure chamber 65 becomes equal to the
pressure of the other pressure chamber 66. When the pressures in both
pressure chambers 65 and 66 are equal to each other, the spool of the
pressure reduction valve portion 24 becomes the blocked position by the
small spring force of the spring 69 to contact the push rod 71 provided on
the spool 64 to the check valve 60. As a result, the pressure of the load
pressure detecting passage 82 becomes equal to the load pressure, and the
pump discharge pressure is controlled at a pressure higher than the
pressure of the load pressure detecting passage 82 in the extent of a
certain pressure difference (e.g. 20 kg/cm.sup.2 ) by the direction
control valve 85 for adjustment of the pump. Since the pump discharge
pressure is introduced into the pump port 44 via the check valve portion
23, the pressure difference (20 kg/cm.sup.2) between the inlet pressure
and the outlet pressure (load pressure) of the direction control valve 22
can be maintained. Accordingly, only by variation of the opening area of a
throttle between the inlet side and the outlet side associated with shift
of the spool of the direction control valve 22, the flow rate of the
pressurized fluid to be distributed to the actuators 88 is controlled.
When the spool of the direction control valve 22 is shifted, the conduit 89
or 90 of the actuator 88 is connected to the second fluid passage 54 for
introducing then load pressure. On the other hand, the second fluid
passage 54 is connected to one pressure chamber 65 of the pressure
reduction valve 24. However, since the load pressure is used only as a
pilot pressure (set pressure of the pressure reduction valve) in the
pressure reduction valve 24, the draining of the pressure will never been
caused. Accordingly, upon shifting the spool of the direction control
valve 22, the natural drop of the actuator 88 due to drop of the load
pressure will never been caused.
The load pressure detecting passage 82 is also connected to the other
pressure chamber 66 of the pressure reduction valve portion 24 of the
pressure compensation valve 25 arranged in the other direction control
valve 22. However, since one pressure chamber 65 of the pressure reduction
valve portion 24 is communicated with the tank 86 by the direction control
valve 22 in the neutral position A, the pressure in the first fluid
passage 53 for introducing the load pressure is held zero, and thus the
spool of the pressure reduction valve portion 24 biases the check valve of
the check valve portion 23 to the valve closing direction by the pressure
of the pressure chamber 65.
On the other hand, in the pressure chamber a generating the pressure for
biasing the check valve of the check valve portion 23 in the valve opening
direction, the discharge pressure of the pump 20 is introduced from the
pump discharge line 21. Therefore, as a whole, with the pressure
difference (20 kg/cm.sup.2) between the pump discharge pressure and the
pressure of the load pressure detecting passage 82, the check valve of the
check valve portion 23 and the spool of the pressure reducing valve
portion 24 are shifted in the valve opening direction of the check valve
60. However, the shift is quite small so that the check valve is opened
with the small spring force of the spring 69 when the pressure of the pump
port 44 reaches the predetermined pressure difference. Accordingly, the
spool of the pressure reduction valve portion 24 will never be shifted to
the stroke end by the pressure in the pressure chamber a of the check
valve portion 23. Therefore, it will never influence for the hydraulic
pressure control by the direction control valve 22.
(3) When Spools of Both Direction Control Valves 22 are in the First
Pressurized Fluid Supply Positions B
(3)-1 When Total of Necessary Flow Rate of Respective Actuators 88 is the
Maximum Discharge Flow Rate of Hydraulic Pump 20
Here, it is assumed that the spools of both of the direction control valves
22 are shifted to the first pressurized fluid supply positions B, and
respective pump ports 44, the conduits 89, the first fluid passages 53 for
introduction of the load pressure are connected.
The spool of the pressure reduction valve portion 24 of the pressure
compensation valve 25 of one of the direction control valves 22 is
maintained at the shifted position at the stroke end until the pressure in
the pressure chamber 66 becomes equal to the pressure of one of pressure
chambers 65 of both pressure compensation valves, and until the pressure
of the pressure chamber 66 of the pressure compensation valve 25 of the
other direction control valve 22 becomes equal to the pressure of one of
the pressure chambers 65 similarly to the former. Here, it is assumed that
among shown two actuators 88, the load pressure of the left side actuator
is greater than the load pressure of the right side actuator. In order to
facilitate the following discussion, it is further assumed that the load
pressure of the left side actuator 88 is 100 kg/cm.sup.2 and the load
pressure of the right side actuator is 10 kg/cm.sup.2. Since the load
pressure detecting passage 82 is connected to the tank 86 via an orifice
91, the pressure of the load pressure detecting passage 82 is held zero
(atmospheric pressure) before the spools of the direction control valves
22 are shifted. Accordingly, respective pressure reduction valve portions
24 may communicate the pump discharge pressure with the pressure of the
pressure detecting passage 82.
When the pressure of the load pressure detecting passage 82 is risen to the
pressure (10 kg/cm.sup.2) of the conduit 90 of the right side actuator 88,
the pressure reduction valve portion 24 of the right side pressure
compensation valve 25 is closed, at first. At this time, the spool of the
pressure reduction valve portion 24 of the left side pressure compensation
valve 25 is held at shifted condition. Therefore, the pressure of the load
pressure detecting passage 82 is risen until it becomes equal to the
discharge pressure (20 kg/cm.sup.2) of the hydraulic pump 20. At this
time, the pressure of the pump port 44 of the direction control valve 22
for the left side actuator 88 is 100 kg/cm.sup.2, the check valve portion
23 of the pressure compensation valve 25 is in the closed condition to be
separated from the pressure reduction valve portion 24.
The spool of the pressure reduction valve portion 24 of the pressure
compensation valve 25 biases the check valve of the check valve portion 23
in the valve closure direction with the pressure difference (20-10=10
kg/cm.sup.2) of two pressure chambers 65 and 66. At this time, the
pressure of the pressure chamber a acting in the valve opening direction
for the check valve 60 of the check valve portion 23, is 20 kg/cm.sup.2
equal to the pump discharge pressure. Therefore, the check valve of the
check valve portion 23 is maintained in open position until the pressure
at the pump port 44 of the direction control valve 22 becomes 10
kg/cm.sup.2. Subsequently, the check valve portion 23 is closed by the
spring 69.
By the direction control valve 85 for adjusting the pump, the pump
discharge pressure is controlled at a pressure (40 kg/cm.sup.2) higher
than the pressure of the load pressure detecting passage 82 in the extend
of the predetermined pressure difference (20 kg/cm.sup.2). Even at this
time, the check valve portion 23 of the higher pressure side pressure
compensation valve 25 is maintained in closed state, and the spool of the
pressure reduction valve 24 is held in the shifted position. Therefore,
the pressure in the load pressure detecting passage 82 is risen to 40
kg/cm.sup.2. On the other hand, the spool of the pressure reduction valve
portion 24 in the lower pressure side pressure compensation valve 25
biases the check valve of the check valve portion 23 in the valve closure
direction with the pressure difference (30 kg/cm.sup.2 ) between the load
pressure detecting passage 82 and the first passage 53 for introducing the
load pressure. As a result, the pressure at the pump port 44 of the lower
pressure side direction control valve 22 is maintained at 10 kg/cm.sup.2.
As set forth above, the pressures in the load pressure detecting passage 82
and the pump discharge pressure are continuously risen. When the pump
discharge pressure reaches the load pressure (100 kg/cm.sup.2) of the
higher pressure side actuator 88, the pressures in two pressure chambers
65 and 66 of the pressure reduction valve portion 24 of the higher
pressure side pressure compensation valve 25 become 100 kg/cm.sup.2. Then,
the pressure reduction valve portion 24 is closed with the small spring
force of the spring 69. Then, the push rod 71 contacts with the check
valve 61 of the check valve portion 23. At this time, the spool of the
pressure reduction valve portion 24 of the lower pressure side pressure
compensation valve 25 biases the check valve in the valve closure
direction with the pressure difference (100-10=90 kg/cm.sup.2) between the
load pressure detecting passage 82 and the first fluid passage 53 for
introduction of the load pressure to maintain the pressure at the pump
port 44 of the lower pressure side direction control valve at 10
kg/cm.sup.2.
By repeating the above-mentioned operation, the pump discharge pressure is
controlled at 120 kg/cm.sup.2 by the pump adjusting direction control
valve 85. At this time, the pressure reduction valve portion 24 of the
higher pressure side pressure compensation valve 25 contacts the push rod
71 thereof to the check valve 60 of the check valve portion 23 with only
small spring force of the spring 69. The check valve portion 23 is opened
by the pressure difference between two pressure chambers a and b to
introduce the 120 kg/cm.sup.2 of the pump discharge pressure to the pump
port 44 of the direction control valve 22. On the other hand, the pressure
reduction valve portion 24 of the lower pressure side pressure
compensation valve 25 maintains the check valve portion 23 in the closed
state with the pressure difference (90 kg/cm.sup.2) between the load
pressure detecting passage 82 and the first fluid passage 53 for
introducing the load pressure. However, at a condition where the pressure
of the pressure chamber a for driving the check valve of the check valve
portion 23 becomes 30 kg/cm.sup.2 (120-90), balance is established in the
check valve portion 23 and the pressure reduction valve portion 24.
Accordingly, the check valve portion 23 and the pressure reduction portion
24 slightly shifts so that the check valve portion 23 lowers the 120
kg/cm.sup.2 of the pump discharge pressure to 30 kg/cm.sup.2.
At this condition, the hydraulic control system balances. Then, the
pressure at the pump port 44 at the higher pressure side direction control
valve 22 becomes 120 kg/cm.sup.2 and the pressure at the pump port 44 at
the lower pressure side direction control valve 22 becomes 30 kg/cm.sup.2.
By this, both of the pressure differences of the inlet pressures and the
outlet pressures in two direction control valves 22, 22 become 20
kg/cm.sup.2. Accordingly, two direction control valves can control the
flow rate of the pressurized fluid to be supplied to the actuators 88, 88
only by the shift.
(3)-2 When Total Necessary Flow Rate of Respective Actuators 88 is Greater
Than or Equal to Maximum Discharge Amount of Hydraulic Pump
Here, the load pressures and the necessary flow rates of the actuators 88,
88 are assumed that 100 kg/cm.sup.2 and 501 cm.sup.3 /min in the left side
actuator 88 and 10 kg/cm.sup.2 and 501 cm.sup.3 /min in the right side
actuator 88. When the maximum discharge amount of the hydraulic pump 20 is
greater than or equal to 1001 cm.sup.3 /min, since the difference of the
inlet pressure and the outlet pressure of the direction control valve 22
can be maintained constant as set forth above, flow rate can be controlled
by the shift of the spools to distribute the flow rate for respectively
501 cm.sup.3 /min.
Next, it is assumed that the maximum discharge amount of the hydraulic pump
20 is 701 cm.sup.3 /min, since the inlet pressures of two direction
control valves 22, 22 are respectively 120 kg/cm.sup.2 and 30 kg/cm.sup.2,
the flow rate of the higher pressure side direction control valve 22 is
decreased to be 201 cm.sup.3 /min. On the other hand, the flow rate of the
lower pressure side direction control valve 22 is maintained at 501
cm.sup.3 /min. Assuming that the shift amount of the spools of two
direction control valves 22, 22 are not varied, the pressure difference
becomes smaller than the predetermined pressure difference (20
kg/cm.sup.2) corresponding to lowering of the pressure difference between
the inlet pressure and the outlet pressure in the higher pressure side
direction control valve 22. Here, assuming that the pressure difference is
decreased to 14 kg/cm.sup.2, namely the inlet pressure in the higher
pressure side direction control valve is lowered from 120 kg/cm.sup.2 to
114 kg/cm.sup.2, since the pressures of two pressure chambers 65 and 66
are maintained at 100 kg/cm.sup.2, lowering of the pressure of the
pressure chamber b of the valve closure direction for the check valve
portion 23 should cause shift of the check valve portion 23 to open
position (stroke end) to reduce the pressure in the pressure chamber a.
Namely, the pump discharge pressure is lowered from 120 kg/cm.sup.2 to 114
kg/cm.sup.2. At this time (when lack of the pump discharge amount), the
pump discharge amount cannot depend on the control of the pump adjusting
direction control valve 85.
On the other hand, the pressures of the pressure chambers 65 and 66 of the
pressure reduction valve portion 24 of the lower pressure side pressure
compensation valve 25 are respectively maintained at 100 kg/cm.sup.2 and
10 kg/cm.sup.2 to bias the check valve of the check valve portion 23
toward the valve closure direction with the pressure difference (90
kg/cm.sup.2). The pressure of the pressure chamber a generating the force
in the valve open direction for the check valve portion 23, namely the
discharge pressure of the pump is lowered to 114 kg/cm.sup.2. Therefore,
the balance is established at the reduced pressure from 30 kg/cm.sup.2 to
24 kg/cm.sup.2 in the pressure chamber b generating the force in the valve
closure direction. Accordingly, the pressure difference between the inlet
pressure and the outlet pressure of the lower pressure side direction
control valve 22 is reduced from 20 kg/cm.sup.2 to 14 kg/cm.sup.2. The
direction control valve 22 reduces the supply flow rate for the lower
pressure side actuator 88 from 501 cm.sup.3 /min corresponding to
reduction of the pressure difference. Corresponding to this, the supply
flow rate for the higher pressure side actuator 88 is increased from 201
cm.sup.3 /min.
Namely, balance of the hydraulic system is established at the condition
where the pressure differences between the inlet pressure and the outlet
pressure of the direction control valves 22, 22 are equal to each other,
and the supply flow rates for both actuators 88, 88 are 351 cm.sup.3 /min.
(4) When Three or More Actuators 88 are loaded for one Hydraulic Pump
When the actuators 88 to be driven hydraulically is more than or equal to
three, the foregoing principle of operation can be achieved by arranging
another pressure compensation valve 25 including the check valve portion
23 and the pressure reduction valve portion 24 the hydraulic pump and the
direction control valve, and introducing the pressure differences in the
valve closure direction of respective pressure reduction valve portions to
the load pressure detecting passage 82.
Next, the second embodiment of the pressurized fluid supply system
according to the present invention will be discussed with reference to
FIG. 5. In the following discussion, the elements common to the first
embodiment will be represented by the same reference numerals to the first
embodiment, and detailed description thereof is neglected for avoiding
redundant discussion to keep the description simple enough.
FIG. 5 shows a valve block 30-1 supplying pressurized fluid for left and
right hydraulic traveling motors. The main spool 49 of the direction
control valve 22 is formed with an intermediate small diameter portion 120
selectively communicating and blocking between the pump port 44 and the
first and second load detection ports 45 and 46.
The third port 43 of the pressure reduction valve portion 24 and the second
pressure chamber 66 are blocked from communication by the spool 64. The
spool 64 is formed with a slip form opening 100 on the outer periphery
thereof for selectively communicating and blocking between the third port
43 and the second port 42. The third port 43 is connected to the load
pressure detecting passage 82.
The blind bore 67 of the spool 64 is formed into a stepped bore. A sheet 68
is formed into a configuration having a blind hole 68a and an annular
recess 68b. The sheet 68 is contacted to an outward stepped portion 67a of
the blind bore 67 to be fixed thereon. Between the sheet 68 and a plug 70,
a spring 69 is disposed. A check valve 101 is biased to the peripheral
edge of the opening of the blind hole 68a of the sheet 68 by a spring 102
to define a pressure chamber 103 between the blind hole 68a and the check
valve 101. The pressure chamber 103 is communicated with the second
pressure chamber 66 via a first orifice 104 and with the annular recess
68b via a second orifice 105. The annular recess 68b opens to the third
port 43 via an orifice 106. A spring chamber 107 of the check valve 101
opened to the second port 42 via an orifice 108. On the other hand, the
first pressure chamber 65 is communicated with the chamber between the
sheet 68 and the check valve 101 via a cut-out portion 109 of the spool 64
and an orifice 110.
FIG. 6 is a section of a valve block 30-2 for supplying a pressurized fluid
for a cylinder of a work implement, such as a boom cylinder, for example.
The third port 43 of the pressure reduction valve portion 24 and the
second pressure chamber 66 are blocked from communication by the spool 64.
The spool 64 is formed with a slit form opening 111 for selectively
establishing and blocking communication between the third port 43 and the
second port 42. The pressurized fluid in the second port 42 is directly
supplied to the load pressure detecting passage 82 from the third port 43.
The second pressure chamber 66 is communicated with the third port 43 via a
damping orifice 112. On the other hand, a pressure chamber 113 defined by
the free piston 68 is communicated with the opening 111 via a damping
orifice 114. It should be appreciated that the pressure reduction valve
portion 24 may be constructed in the construction shown in FIG. 3.
By the construction set forth above, when the spool 64 slides in left and
right, the pressurized fluid in the second pressure chamber 88 flows into
the second pressure chamber 88 via the damping orifice 112. Therefore,
abrupt shifting of the spool 64 toward right can be prevented. Similarly,
when the spool 84 is shifted toward left, the flow of the pressurized
fluid opposite to the above is generated to prevent abrupt motion of the
spool.
FIG. 7 shows an example of a hydraulic system incorporating the valve
blocks 30-1 and 30-1 for supplying pressurized fluid for left and right
hydraulic traveling motors illustrated in FIG. 5 and the valve block 30-2
for supplying the pressurized fluid for the work implement cylinder
illustrated in FIG. 6. The second ports 42 in the pressure reduction
valves 24 of the left and right valve blocks 30-1 are communicated with
the passage 115. The first and second actuator ports 34 and 35 of these
two valve blocks 30-1 are respectively connected to the hydraulic motors
as the actuators 88. On the other hand, the discharge line 21 of the
hydraulic pump 20 is respectively connected to the first ports 39 of
respective valve blocks 30-1 and 30-2. Furthermore, the second port 42 of
the valve block 30-2 for supplying the pressurized fluid to the work
implement cylinder is also connected to the discharge line 21 of the
hydraulic pump 20. The third ports 43 of respective valve blocks 30-1 and
30-2 are connected to the load pressure detecting passage 82,
respectively.
Next, discussion will be given for the operation of the hydraulic system in
the construction illustrated in FIG. 7.
Straight Traveling
When the main spools 49 of the direction control valves 22 of respective
valve blocks 30-1 are slide for shift toward left, the discharged
pressurized fluid from the hydraulic pump 20 flows into one of the ports
88a of the actuator 88 via the first port 39, a intermediate small
diameter portion 120, a left side cut-out portion 121, the first load
detection port 45, a communication passage 122, the second load detection
port 46, the left side cut-out portion 123, the second small diameter
portion 51 and the second actuator port 35 as shown in FIG. 5. On the
other hand, a recirculating fluid from the other port 88b flows into the
first tank port 47 via the first actuator port 34, the first small
diameter portion 50 and the first tank port 47 via the first actuator port
34, the first small diameter portion 50 and a left side cut-out 124.
The load pressure of the hydraulic motor as the actuator 88 acts in the
first pressure chamber 65 via the second actuator port 35, the second load
detection port 46 and the passage 58 to push the spool 64 toward right for
shift.
At this time, the pressure in the second port 42 acts on the left side
surface of the check valve 101 as introduced into the spring chamber 107
of the check valve 101 via the orifice 108.
On the other hand, into the pressure chamber 103 between the check valve
101 and the blind bore 68a, the pressure of the third port 43 is
introduced through the orifice 105 to act the hydraulic force to the right
side surface of the check valve 101. Since the pressure at the second port
42 and the pressure at the third port 43 are the same, the check valve 101
is seated on the sheet 68 by the spring force of the spring 102.
By this, the cut-out groove 109 of the spool 64 opens to the second port 42
as shown in FIG. 7. Then, for communication through the orifice 115, the
load pressures of the left and right hydraulic traveling motors as the
left and right actuators 88 connected to the left and right valve blocks
30-1 become equal to each other by communication through the second port
42 and the orifice 115. Furthermore, since the second port is communicated
with the third port 43 via the opening 100, the flow rate to be supplied
to respective one port 88a of the left and right actuators 88 becomes
equal to each other to permit straight travel.
In the above-mentioned traveling condition in straight, if the main spool
49 of the direction control valve 22 of the valve block 30-2 for supplying
the pressurized fluid to the work implement cylinder is slide toward left,
as shown in FIG. 6, the discharge pressurized fluid of the hydraulic pump
20 is supplied to an expansion side pressure chamber 88c of the work
implement cylinder via the second actuator port 35 from the first port 39
of the valve block 30-2. At this time, the pressurized fluid in a
contraction side pressure chamber 88d is recirculated to the first tank
port 47 from the first actuator port 34.
At this time, since the actuation load of the work implement cylinder, such
as boom lifting-up load and so forth becomes greater than the traveling
load, the discharge pressure of the hydraulic pump 20 is risen to increase
the pressure in the expansion side pressure chamber 88c of the work
implement cylinder serving as the actuator 88. The increase pressure acts
on the first pressure chamber 65 of the spool 64 of the pressure reduction
valve 24 to urge the spool 64 toward right to cause sliding of the spool
60 of the check valve portion 23 toward right. Therefore, the discharge
pressure of the hydraulic pump is further increased. The discharge
pressure of the hydraulic pump 20 acts on the second pressure chamber 66
via the second port 42, the opening 111, the third port 43 and the damping
orifice 112 to urge the spool 64 toward left to push the spool 60 of the
check valve portion 23 via the push rod 71. Accordingly, the discharge
pressure of the hydraulic pump becomes the pressure corresponding to the
load pressure by the work implement load.
By this, a control pressure corresponding the load pressure of the work
implement cylinder is introduced into the third port 43 of the pressure
reduction valve portion 24 of the left and right valve blocks 30-1 from
the load pressure detecting passage 82, and then introduced into the
second pressure chamber 66 via the orifice 106 of the spool 64, the second
orifice 105 of the sheet 68, the pressure chamber 103 and the first
orifice 104.
Here, since the traveling load pressure is smaller than the working load
pressure, the pressure of the pressure chamber 65 becomes lower than the
pressure of the second pressure chamber 66 to cause shift of the spool 64
toward left.
At the same time, by the control pressure in the pressure chamber 103, the
check valve 101 is exerted the force in the valve open direction against
the spring force of the spring 102. In the spring chamber 107 of the check
valve 101, a pressure corresponding to the traveling load of the second
pressure chamber acts. Since this pressure is smaller than the control
pressure, the check valve 101 opens to permit the control pressure to flow
into the first pressure chamber 65 of the spool 64 via the orifice 110 and
the cut-out groove 109. The control pressure is bypassed through the
passage, the second load pressure detecting port 48 and the second
actuator port 35 to the side of the traveling motor.
By this, the control pressure is lowered. Therefore, the discharge amount
of the hydraulic pump 20 is not significantly reduced so as to prevent
abrupt reduction of the flow rate to be supplied to the left and right
hydraulic traveling motors. Accordingly, even when the work implement
cylinder performed loaded operation, such as lifting-up of the boom during
travel, occurrence of significant deceleration shock can be successfully
avoided.
Left or Right Turning
When the main spool 49 of the direction control valve 22 of the right side
valve block 30-1 shifts in rightwardly toward the neutral position during
travel in straight, the open areas of the second load pressure detection
port 46 and the second actuator port 35 are reduced to decrease the flow
rate of the working fluid flowing into one port 88a of the right side
actuator 88.
As a result of this, the load pressure of the right side actuator 88 is
lowered. Lowering of the load pressure in the right side actuator 88
causes lowering of the pressure in the first pressure chamber 65 of the
pressure reduction valve portion 24 of the right side valve block 30-1.
Then, the spool 64 is urged toward left by the load pressure (control
pressure) of the second pressure chamber 66 of the left side valve block
30-1, which is supplied through the load pressure detection passage 82 of
the second pressure chamber 66. Then, communication between the second
port 42 and the first pressure chamber 65 via the cut-out groove 109 is
blocked. As a result, the load pressures at the left and right sides
becomes not equal to each other. Thus, the load pressure at the right side
actuator 88 becomes lower and the load pressure at the left side actuator
88 becomes high to cause right turn on the vehicle.
At this time, the load pressure of the hydraulic motor acting as the left
side actuator 88 is introduced into the spring chamber 102 of the check
valve 101 of the pressure reduction valve portion of the right side valve
block 30-1 via the passage 115, the second port 42 and the orifice 108.
Then, the load pressure acts on the left side surface of the check valve
101.
On the other hand, the control pressure acts on the right side surface of
the of the check valve 101 via the load pressure detecting passage 82, the
third port 43, the orifice 106 of the spool 84 and the second orifice 105.
The control pressure is substantially equal to the load pressure of the
left side hydraulic traveling motor. The check valve 401 becomes the state
contacting with the free piston 68.
Comparing the second embodiment of the pressurized fluid supply system with
the first embodiment of the system, in the first embodiment of the
pressurized fluid supply system, a flow rate proportional to the open
areas of the first and second pressure detection ports 45 and 48 and the
first and second actuator ports 34 and 35 is supplied to the first and
second actuator ports 34 and 35 irrespective of the load pressure in the
actuator 88. Therefore, in the case where the pressurized fluid is
supplied to the left and right traveling motors of a hydraulically driven
vehicle, it is possible to cause curve traveling instead of straight
traveling when the flow rates supplied to be supplied to the left and
right hydraulic traveling motors are differentiated due to tolerance of
the open areas of the left and right direction control valves. Therefore,
high precision is required in machining the direction control valve.
Furthermore, in the first embodiment of the pressurized fluid supply
system, the maximum load pressure (control pressure) of the load pressure
detecting passage 82 is exerted to the pump adjusting direction control
valve 85 to adjust the discharge amount of the hydraulic pump 20 to
increase and decrease depending upon the discharge pressure of the pump,
to control the absorbing torque of the hydraulic pump and whereby prevent
excessive load on the engine driving the hydraulic pump. For example, as
shown in FIG. 4, as shown by A, when the discharge pressure of the pump
becomes higher than or equal to the predetermined value P.sub.x, the pump
discharge pressure is decreased when the control pressure becomes higher
than or equal to the predetermined pressure P.sub.x.
On the other hand, in the case where the first embodiment of the
pressurized fluid supply system supplies the pressurized fluid to left and
right hydraulic traveling motors of a power shovel and the work implement
cylinder, and when the work implement is actuated by supplying the pump
discharged pressurized fluid to the work implement cylinder under the
condition of traveling by supplying the pump discharged pressurized fluid
to the left and right hydraulic traveling motors, the control pressure is
risen with causing reduction of the pump discharge amount to cause abrupt
drop of the traveling speed to generate significant deceleration shock
since the load pressure of the work implement cylinder becomes greater
than the load pressure of the left and right hydraulic traveling motors.
For instance, in FIG. 4, the load pressure (pump discharge pressure) of
the left and right hydraulic traveling motors while traveling varies
according to traveling resistance characteristics B which is lower than
the predetermined pressure P.sub.x, so the pump discharge amount increases
to Q.sub.1. However, when the work implement cylinder is operated at a
pressure where a relief valve is active for relieving extra pressure, the
load pressure (pump discharge pressure) becomes maximum pressure P.sub.y
to reduce the pump discharge amount to Q.sub.2.
In contrast to this, in the construction of the second embodiment, when the
main spools 49 of the direction control valves 22 of the left and right
blocks 30-1 are operated simultaneously in the same direction to supply
the pressurized fluid of the hydraulic pump to the first and second
actuator ports 34 and 35, the spools of respective pressure reduction
valve portions 24 are depressed in the direction against the spring forces
with the pressures of the first pressure chambers to establish
communication between the first pressure chambers 65 and the second port.
Then, the pressures of the second ports 42 of the left and right valve
blocks 30-1 become equal to each other to supply the same flow rate of the
pressurized fluid to the left and right actuators 88 even when the open
area of the direction control valve 22 of the left and right valve blocks
30-1 are differentiated to each other due to tolerance.
Furthermore, in the second embodiment of the pressurized fluid supply
system, when the main spool 49 of the direction control valve 22 of the
valve block 30-2 is shifted to supply the discharged pressurized fluid of
the hydraulic pump 20 to the work implement cylinder while the discharged
pressurized fluid of the hydraulic pump 20 is supplied to the left and
right hydraulic traveling motors from the left and right valve blocks
30-1, and when the load pressure of the work implement cylinder is higher
than the load pressure of the left and right hydraulic traveling motors,
the control pressure higher than the load pressure of the left and right
traveling motors is generated at the third port 43 of the pressure
reduction valve portion 24 of the valve block 30-2. The control pressure
flows into the third ports 43 of the left and right valve blocks 30-1 to
open the check valves 101 to introduce the controlled pressure to the
second pressure chambers 66 through the communication hole. Through the
second pressure chambers 66, the control pressure is by-passed to the left
and right hydraulic traveling motors to lower the control pressure.
Therefore, even when the work implement is operated during travel, the
control pressure becomes lower than the pressure corresponding to the work
implement load to avoid excessive reduction of the discharge amount of the
hydraulic pump 20. Accordingly, the flow rate of the pressurized fluid to
be supplied to the left and right hydraulic traveling motors will never
varied abruptly, the deceleration shock can be reduced.
In the valve blocks 30-1 and 30-2 shown in FIGS. 5 and 6, by forming a
small diameter section 150 on the spool of the check valve portion 23 for
selectively establishing and blocking communication between the first port
39 and the pump port 44, and define the pressure chamber 151 for urging
the spool 60 toward right in the drawing and the first port to communicate
the pressure chamber 151 to the first port 39 via a damping orifice 152
and a communication hole 153. By this, when the spool 60 is shifted toward
left and right, the pressurized fluid flows between the first port and the
pressure chamber 151 via the damping orifice 152, abrupt behavior of the
spool in the left and right direction can be avoided.
FIG. 8 shows a cross section of a multiple valve constructed by coupling a
plurality of valve blocks with mating front and read faces. In the shown
embodiment, there is illustrated an example where first to sixth valve
blocks 30a to 30f are provided.
In the shown example, the second and third valve blocks 30b and 30c
correspond to the valve blocks 30-1 for supplying the pressurized fluid to
the left and right hydraulic traveling motors of FIG. 5, and the fourth
valve block 30d forms the valve block for supplying the pressurized fluid
for the work implement cylinder. To the first valve block 30a, a first end
block 130 is coupled. In the first end block 130, a primary fluid bore 131
connected to the first port 39 is formed. The primary fluid bore 131 is
communicated with a fluid bore 133 via a check valve 132. The fluid bore
133 is communicated with the second port 42 of the first valve block 30a
via a port 134. The third ports 43 of respective valve blocks 308 to 30f
are communicated with each other. The second ports 42 of the second and
third valve blocks 30b and 30c are mutually communicated via a port 136.
Similarly, the second ports 42 of the fourth, fifth and sixth valve blocks
30d, 30e and 30f are mutually communicated through a port 137. Also, the
first ports of all valve blocks 30a to 30f are communicated with each
other through the primary fluid bore 131.
In the sixth valve block 30f, a second end block 139 is coupled. The second
end block 139 is formed with a first communication passage 140 and a
second communication passage 141 are formed. The first communication
passage 140 is communicated with the first port 39 and the second port 42
of the sixth valve block 30f via a port 142. The second communication
passage 141 is communicated with the third port 43 and the load detection
passage 82 via a port 143.
FIGS. 9 to 11 show the preferred construction of the multiple valve shown
in FIG. 8. In FIGS. 9 to 11, a valve body 201 is formed with a pump
passage 207, a main passage 208 and a tank passage 209. The valve block
200 is formed with a threaded hole 213 for a stud bolt in one side surface
200a mating with one side surface 201a of the valve body 201, and a
threaded hole 214 for a cover bolt on the other side surface. A stud bolt
204 extends through one valve block 200 and the valve body 201 and is
threadingly engaged to the threaded hole 213 of the other valve block 200
to rigidly connect therebetween. For the other valve block 200, a cover
215 is mounted by threadingly engaging a cover bolt 216 to the threaded
hole 214 therefor. It should be noted that, in the drawings, the reference
numeral 203 denotes a spool, 203a denotes a spool bore, 205 denotes a
mounting screw for mounting the valve block 200 and the valve body to a
mounting portion 206 for mounting the multiple valve.
The other valve block 200 is formed with an inlet port 210 and a tank port
212 extending through one side surface 200a to the other side surface
200b. On one side surface 215a of the cover 215, a cut-out groove (or
passage) 218 communicating an inlet passage 207 and a main passage 208 is
formed.
Next, manner of adding one valve block after assembling the multiple valve
constructed as set forth above will be discussed with reference to FIGS.
12 to 14.
At first, the cover bolt 216 is loosened to remove the cover 215. Then, the
valve body 201 of the valve block to be added is arranged at the other
side 200b of the other valve block 200. Through a bolt hole 217 extending
between both side surfaces 200a and 200b of the valve body 201, a longer
cover bolt 216 is inserted and engaged to the threaded hole 214 for the
cover bolt on the other surface 200b of the other valve block 200. Thus,
the valve body 201 of the new valve block 200 is fixed to the other side
surface 200b of the other valve block 200. Finally, on one side surface
201a of the newly mounted valve body 201, the cover 215 is mounted. By
this, the inlet port 210 of the newly added valve block and the main port
211 are communicated through the cut-out groove 218 formed in the cover
215.
Since the multiple valve constructed as set forth above permits mounting of
the valve body of the valve block to be added on the other side surface of
one valve block when the valve block is added after assembling, the
following advantages can be achieved:
(1) it is not necessary to exchange the stud bolt to longer one;
(2) it is not necessary to loosen the stud bolt and the condition of mutual
connection of the valve body is not varied so that leakage of the fluid
through the connecting portion cannot be caused;
(3) it is not necessary to disassemble after assembling, straightness,
circularity of the spool will not be varied so that smooth action of the
spool can be attained;
(4) since disposition of the valve block will never be caused, it is not
necessary to modify the piping positions to the inlet port and the tank
port; and
(5) since the mounting hole for one valve block will not cause disposition,
it is not necessary to vary the position of the bolt hole in the mounting
portion.
Although the invention has been illustrated and described with respect to
exemplary embodiment thereof, it should be understood by those skilled in
the art that the foregoing and various other changes, omissions and
additions may be made therein and thereto, without departing from the
spirit and scope of the present invention. Therefore, the present
invention should not be understood as limited to the specific embodiment
set out above but to include all possible embodiments which can be
embodies within a scope encompassed and equivalents thereof with respect
to the feature set out in the appended claims.
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